Cleaving GaAs and similar materials is a method which has been disclosed in IBM Technical Disclosure Bulletin, Vol. 23, No. 10, (March 1981), pp. 4749-4750. It involves scribing a wafer surface and then controllably bending the wafer so that it fractures along the scribed lines. Among the operative conditions disclosed as necessary, the following are of relevance:
To cleave a bar of given length L, the wafer should be thinner than L/2.
The scribed wafer should be bent in such manner that the plane of the bending radius is normal to the scribed lines on the convex side of the wafer.
The wafer must be mounted on a substrate which is sufficiently rigid so as to support the wafer, yet it must also be deformable to the necessary bending radius and should also be located on the concave side of the wafer when bent.
The convex side of the wafer must be constrained in order to prevent stress from being applied to the side of the wafer adjoining the substrate so as to prevent the wafer from separating from the substrate. A flexible material can be used to cover the wafer and the substrate.
A sandwich of the substrate, wafer and flexible upper foil must be joined by flexible adhesives which are readily removable and which will damage the cleaved pieces.
Non-rigid adhesive sheets are known in the art of processing semiconductor wafers. They are designed for use in holding semiconductor wafers firmly in place, e.g., while breaking processes are performed thereon. They are generally used in a sandwich comprised of a non-rigid PVC-foil and a polyester foil joined together by means of an acrylic adhesive. Such adhesives are available, for instance, from Nitto Electric Industrial Co., Ltd. (Japan). The adhesion of such foils to each other in the sandwich is about 100 to 350 N/m, depending of the type of sheet and the duration of its storage.
A device suitable for breaking a plate-like workpiece sandwiched between two flexible foils of a sheet of the above indicated kind is known in the art and available for instance from Dynatex Corporation (U.S.A.). This known device is comprised of a movable cross-table having a wafer affixable thereon and utilizes a wedge and an anvil therefor. The cross-table has an aperture adapted to be overlaid by the properly oriented wafer. The wedge is made to press the wafer against the anvil through the aperture. The anvil being made of hard rubber so as to be slightly resilient.
Using such know apparatus, the process of breaking a wafer comprises the steps of: scribing one of the workpiece surfaces with at least one scribing line in order to define a plane where the workpiece is to be broken; placing the workpiece, with its scribed surface facing upwards between an upper and lower foil, both foils being flexible and extending beyond the margins of the workpiece, an adhesive serving to join the workpiece to the lower foil; applying an upward force to the lower side of the sandwich structure in order to bend the workpiece, the plane of the radius being normal to the scribed lines on the convex side of the workpiece, so that the workpiece breaks into individual bars as determined by the scribed lines; and removing the upper foil whereafter the lower foil can be stretched so that the individual bars become separated and can be taken from the lower foil for further processing. However, known devices and methods of breaking a wafer are not specifically designed and adapted for the manufacture of semiconductor lasers whose mirror facets are obtained as cleavage planes of the semiconductor wafer. One reason is that these mirror facets are very fragile and very often become damaged by crushing between adjacent laser elements before the latter becomes separated by stretching the lower foil. Further known devices are also extremely costly in that the cross-table must be moved while the wafer is observed under a microscope in order to precisely position the wedge and anvil at each scribed line in succession. The wedge must be precisely operated.